THE INTERBRAIN OR THALAMENCEPHALON. 



135 



center which is inserted in between an important part of the cerebrum and 

 nearly all other parts of the brain. 



Traces of a progressive development of the thalamus are found in the 

 reptiles, where from the frontal cerebral cortex a bundle arises which, end- 

 ing in the thalamus, represents a direct cortico-thalamic tract. In birds 

 the same thing is even more evident, and one may recognize how, with the 

 development of an extended cerebral cortex, more and more bundles appear 



Tr. oooipito-tectalis 

 Commis. aut. 



Tr. strio-thal. niedialis 



Tr. atrio-tlial. lat, 

 Tr. septo-meaenoe^ 

 phalicus 



Nucleus rotundus'l ~ , ' 



thai ami J — ; — . 



Median opticus liun-S 



die to the ganglion >- 



isthmi^ 



Partes corp. genie, lat. 



Decussation of the"! 



Anterior cerebellar >- 



pedunclesj 



Tr. tegnientol . — 



cerebellHrisJ 

 Corpus restiforme 



Fillet — ■ 



Tr. thalamo-tectalis ■ — - 



N. oculo-motorius " 



I -±.... 



Fig. 84. — Sagittal section througli the Thalamus opticus of the domestic 

 pigeon. Hsematoxylin staining. 



which pass from it into the ganglia of the thalamus. In mammals these 

 Tr. cortico-thalamici have imdergone such a great development that they 

 make the greatest system of the thalamencephalon^ and taken together are 

 designated Corona radiata of the Thalamus. With this transformation there 

 goes hand in hand a gradual enlargement of the ganglia; so that it is no 

 longer possible to recognize the comparatively simple relations which exist 

 in reptilia and to homologize with certainty the large thalamic nuclei of 



